I've never heard of selling or re-filling one that shoots "slime", maybe outside of a kid's toy version, but for anyone else curious about them:
1) Firefighting foam can be pretty bad for you - depending on composition, the extinguishers can be filled with any variety of irritants or toxic chemicals.
2) Seriously: Avoid powder/dry chemical extinguishers like the one pictured altogether; You may die if that shit gets in your lungs.
You may, however, be looking for Avalanche Foam. You can get it through Messy Supplies, it's non-toxic, and I think they have a toy gun squirt...thing... you can dispense it with. It's probably the closest to what you're looking for.
It's so much more complicated than it sounds. In stage, film and TV it's usually a task sub-contracted out to prop making/visual effects professionals as each individual application tends to bring up its own set of problems and solutions. Many of the most effective solutions involve a gutted or fake extinguisher hiding some form of mechanical propulsion device involving compressed air or Co2.
Refilling a liquid extinguisher (and its appropriate propellant) is a specialised service sold as part of a rental or purchase contract and not an easy thing to do at home unless you've got a very well equipped workshop and you're very mechanically adventurous and/or competent. Certainly not a casual task.
I spent some time a few years ago creating a compressed air device for propelling gunge and paint safely using a compressor that was never fully realised before I gave up my studio space. If I resume producing it will most certainly make an appearance!
It's a good topic, though (like gunge tank building), for discussion.
Love you, too
